Eur. Phys. J. B (2012) 85: 46
https://doi.org/10.1140/epjb/e2011-20567-1

Regular Article

Magnetic near fields as a probe of charge transport in spatially dispersive conductors

Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany

^a e-mail: haakh@uni-potsdam.de

Received: 12 July 2011
Received in final form: 26 October 2011
Published online: 25 January 2012

Abstract

We calculate magnetic field fluctuations above a conductor with a nonlocal response (spatial dispersion) and consider a large range of distances. The cross-over from ballistic to diffusive charge transport leads to a reduced noise spectrum at distances below the electronic mean free path, as compared to a local description. We also find that the mean free path provides a lower limit to the correlation (coherence) length of the near field fluctuations. The short-distance behaviour is common to a wide range of materials, including semiconductors and superconductors. Our discussion is aimed at atom chip experiments where spin-flip transitions give access to material properties with mesoscopic spatial resolution. The results also hint at fundamental limits to the coherent operation of miniaturised atom traps and matter-wave interferometers.